The present invention relates to double-metal cyanide (DMC) catalysts for preparing polyether polyols by the polyaddition of alkylene oxides on to starter compounds having active hydrogen atoms.
DMC catalysts for the polyaddition of alkylene oxides on to starter compounds having active hydrogen atoms are known. See, for example, U.S. Pat. Nos. 3,404,109; 3,829,505; 3,941,849; and 5,158,922. In comparison to polyether polyols prepared with alkali catalysts such as, for example, alkali metal hydroxides, DMC-catalyzed polyether polyols exhibit a reduction in the content of mono-functional polyethers having terminal double bonds, so-called xe2x80x9cmono-olsxe2x80x9d. Polyether polyols prepared with DMC catalysts can be used to produce high-grade polyurethanes such as, for example, elastomers, foams and coatings.
DMC catalysts are typically prepared by reacting an aqueous solution of a metal salt with an aqueous solution of a metal cyanide salt in the presence of an organic complexing ligand, for example, an ether. In a typical DMC catalyst preparation, aqueous solutions of zinc chloride (in excess) and potassium hexacyanocobaltate are mixed together to form a suspension. Dimethoxyethane (glyme) is then added to the suspension. The DMC catalyst is then filtered and washed with an aqueous solution of glyme. A DMC catalyst prepared in this manner can be represented by the general formula:
Zn3[Co(CN)6]2.xZnCl2.yH2O.zglyme
See, for example, EP-A 700 949.
The following references disclose DMC catalysts which use tert-butanol as the organic complexing ligand (by itself or in combination with a polyether) in the preparation of polyether polyols to further reduce the content of mono-ols: JP 4145123; U.S. Pat. No. 5,470,813; EP 700 949; EP 743 093; EP 761 708; and WO 97/40086. Additionally, the use of these DMC catalysts in the production of polyether polyols reduces the induction time in the polyaddition reaction of alkylene oxides with corresponding starter compounds. Catalytic activity also increases with the use of these DMC catalysts.
There remains, however, a need for DMC catalysts which have increased activity compared to catalysts known in the art which can be used to produce polyether polyols.
DMC catalysts of the present invention are composed of: a) at least one DMC compound; b) at least one organic complexing ligand which is not a cyclic polyol; and c) at least one cyclic polyol.
DMC catalysts of the present invention have increased activity compared to catalysts known in the art.